There has been known a mobile crane including a travelable crane main body and a counterweight carrier capable of traveling following the crane main body. The counterweight carrier is coupled to the crane main body via a coupling member. The counterweight carrier is mounted with a counterweight to increase stability of the crane main body by the weight of the counterweight and improve a hoisting ability of the crane main body.
As such a mobile crane, Japanese Unexamined Patent Publication No. H5-208796 discloses a mobile crane including a lower traveling body, an upper swing body mounted on the lower traveling body to be capable of swing, and a counterweight carrier coupled to a rear part of the upper swing body via a coupling member. The lower traveling body and the upper swing body configure a crane main body. The lower traveling body self-travels according to operation of an operation lever for traveling. The counterweight carrier includes a plurality of wheels and a carrier traveling motor. The carrier traveling motor drives to rotate the wheels according to the operation of the operation lever to thereby enable the counterweight carrier to travel following the crane main body.
The traveling of the counterweight carrier is performed by, for example, driving of the wheels by a hydraulic motor. However, depending on loadage of a counterweight on the counterweight carrier, it is likely that a driving pressure for the driving is excessive or insufficient. Specifically, if the loadage of the counterweight on the counterweight carrier is large, it is likely that the driving pressure is relatively insufficient and the counterweight carrier cannot normally travel. Conversely, if a large driving pressure is set assuming that the loadage of the counterweight on the counterweight carrier is the largest, a loss of energy consumed for the driving is large. It is likely that it is difficult to synchronize a movement of the counterweight carrier with a movement of the crane main body because the driving pressure is excessively large.